In their first 4 years of language learning, children acquire roughly 15000 words. Understanding how they acquire so many words so quickly is fundamental to understanding a critical aspect of human cognition: how natural predispositions interact with learning mechanisms to carve the world into the categories encoded by language. Answering this question is in turn a prerequisite for understanding disorders in language development and the commonly observed links between language disorders and other learning disabilities. In this research, we investigate a "shape bias" in children's early word learning. As first reported by Landau, Smith, & Jones (1988), 2- and 3 year-old children who are given a novel name for a novel object extend the name to other objects that are the same shape as the exemplar, regardless of variations in texture and size. We believe that the shape bias provides an important new window on the mechanisms of word acquisition and especially the interaction of perception, language, and knowledge in first language learning. The present research consists of 9 experiments directed to three objectives: (1) Tracking the developmental origins of the shape bias, in interactions between object knowledge, perception, and language. Five experiments examine the shape bias in children 16 months to 5 years of age. We are specifically interested in how the perceptual properties of rigid objects and language might interact to create and refine the shape bias. (2) Challenging the shape bias: two experiments examine the "moveability" of the shape bias in children from 24 to 48 months of age. These experiments follow up on previous findings that the shape bias is at first fragile, then strong and rigidly applied, then more flexible and differentiated. (3) The shape bias and category induction: two experiments ask whether newly-formed categories based on shape will support children's induction. Such inductions provide an important mechanism for the growth of category knowledge. In the core method, children are presented with novel 3-dimensional objects, made of wood, wire, or cloth. The object is named. The children then decide whether other objects can be called by the same name. This method duplicates the natural context of first word acquisitions.